Universiteit Leiden

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Using tweezers of light to study the misfolding proteins of muscular diseases

Alireza Mashaghi from the Leiden Academic Centre for Drug Research (LACDR) will use state-of-the-art technology to investigate proteins that play a role in muscular dystrophy. His goal is to provide new insights for designing novel therapeutic strategies in the future. To accomplish this, Mashaghi receives the competitive Personal Grant from the Muscular Dystrophy Association in the United States of America.

Misfolding proteins

Mashaghi is dedicated to unravel the underlying mechanisms of PolyQ diseases. The cause of these severe muscular diseases lies in misfolding proteins. Proteins are tiny molecular chains responsible for most cellular functions. These chains need to fold in a certain way in order to form functional molecular machines. For a protein to function, the chain should fold correctly and the folded parts should move with respect to each other in order to conduct the desired task. Sometimes, this goes wrong. ‘When proteins misfold or folded parts fail to move properly, protein misfolding diseases occur’, explains Mashaghi. PolyQ disease are a class of such misfolding disorders, which are progressive and cause impaired coordination. At present, there are no treatment options for these debilitating neuromuscular conditions.

Optical tweezers, a technology that has recently been recognised with the 2018 Nobel Prize, enable direct observation of the folding defects in single proteins. ‘They thereby provide a unique tool for revealing the mystery of PolyQ diseases. With the support of Muscular Dystrophy Association (MDA), we would like to introduce this new technology to the field of PolyQ diseases.’

Optical tweezers

Optical tweezers serve as actual tweezers but on a microscopic scale. They consist of a highly focused light beam that uses light to manipulate objects as small as a single atom. The attractive or repulsive forces provided by this beam can hold and move a microscopic particle.

Optical tweezers can be used to trap all kind of particles, such as viruses, bacteria, cells, metal particles and even strands of DNA. Applications include confinement and organisation (for instance for cell sorting), tracking of movement (of bacteria), application and measurement of small forces, and altering of larger structures (such as cell membranes).


‘We will focus on a special type of messenger protein called the Androgen Receptor (AR)’, tells Mashaghi. ‘The mutant form of this protein is responsible for Spinal Bulbar Muscular Atrophy (SBMA), also known as Kennedy’s disease.’ The toxic mutant protein disrupts hormone-dependent signalling and causes degeneration of neurons that control our muscles, muscle weakness and an insensitivity to male hormones. Mashaghi: ‘This progressive disease with no known cure can reduce the quality of life and life expectancy through weakened or paralysed muscles, including the respiratory muscles. Despite the severity of this disease it is still unclear how the deformed protein exactly affects different tissues of the patient.’

Probing chances

Mashaghi believes the adding of a certain amount of extra ‘beads’ (amino acids called glutamines) to an AR protein chain causes the problems. Because of the extra amino acids, the folding dynamics of the protein change dramatically. This results in altered signalling and SBMA-symptoms in the affected tissues. ‘Testing this hypothesis is challenging as these molecular changes are very subtle and often not visible using conventional techniques. We will use the start-of-the-art optical tweezers technology to zoom into one single AR protein and to directly track the changes.’ Since 2009, Mashaghi has been involved in developing the technology. Recently, he applied it to study some simple model proteins. ‘We are now ready to take a major step forward, and to study the complex disease-related human protein, AR,’ he says proudly. 

Zooming in

And that pride is not unjustified. The grant review process of the MDA is very competitive; only the top 10% of all proposals typically receive support. The MDA grant therefore represents a strong vote of confidence on the merits of a proposal and the capabilities of your research team. ‘We will zoom in on the most critical step in the emergence of the disease which has never been studied directly.’ Mashaghi and his team hope to be able to directly track down the molecular defect that presumably underlies the disease process. ‘The knowledge gained from this project can feed the design of new therapeutic strategies in the future for SBMA, but also for many other related diseases.’

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